Ok, I'm decided to post this here just because after searching for refraction of light, I see alot of posts in this category. Currently in my Physics class, we're working on the theory of light in the book, Newton to Einstein the trail of light. After covering refraction and snell's law to calculate refraction of a crest of light when it passes from one substance to another, I found another way to calculate the refraction without Snell's law. Please comment on what I have here as I can't seem to locate any information regarding it. 1. The problem statement, all variables and given/known data Hopefully my attachment will work, it's a Word file I just drew. The first sketch shows a light wave at one instance in time heading toward a certain transparent solid. The speed of light in the solid is 2 x 10^10 cm/second. In a vacuum it's 3 x 10^10 cm/second. We were supposed to reproduce the sketch and add the crest line as it would appear 10^-10 seconds later, ignoring the reflected line. 2. Relevant equations I roughly drew out Snell's law where one is supposed to find the angle of incidence (i in the drawing) the a perpendicular line towards the solid one wavelength long. where it touches the boundry line, the refracted crestline would be drawn at the angle of refraction as calculated by Snell's law using the Index of refraction of the two substances and so on which you can draw a perpendicular line from this line to the boundary line which would measure one wavelength of the light in the solid. 3. The attempt at a solution My thoughts were, since with the given information in the problem, we don't know the angle of incidence or the index of refraction for the substances (although they could easily be calculated) why not use the crest line given and draw two perpendicular lines from it into the solid, one from point B would be 3cm long since it would travel that far in the given time in air and from point A 2cm long since in the solid the light would travel that distance. The the new crest in air would remain parallel to the old crest and the point at the boundary line would then be used to draw the crest line in the solid along with the point 2cm in. I have drawn this up many different times using Snell's law and different angles checking it with merely drawing the distance lines as I've shown and the results are very nearly accurate if not accurate, Exact measurements with a cheap protrator and ruler are hard to acheive as well as duplicate. Just my thinkings on this, please comment with what you think. In class, going over this problem, my instructor actually began solving the problem just as I described until another student said snell's law must be used, according to the book. After looking at the problem for a minute, he changed his method to use Snell's law. The next day before class, I showed him the sketches I'd made, telling him I agreed with how he initially began the problem and felt it a viable route. He seemed to stick with Snell's law stating that he had mispoke before.